The art of inductively coupling an induction heating coil with a ferrous utensil, thereby electromagnetically heating the contents of the utensil, has been widely known for many years. Additionally, many such prior art arrangements have included sensing arrangements for determining whether the utensil is placed on the cooking surface above the heating coil before the coil is powered. These sensing arrangements reduce the likelihood that high strength electromagnetic fields generated by the heating coil will be leaked into the space surrounding the cooking surface during periods when a proper load is not located on the cooking surface.
Various sensors have been used for this purpose. For example, U.S. Pat. No. 3,796,850-Moreland II et al utilizes a reed switch coupled to two magnets. If no utensil is placed over the induction heating unit, the contacts of the reed switch are forced to close due to the magnetic flux lines produced by the magnets. However, if a utensil is placed over the induction heating unit, the magnetic flux lines are not sufficiently strong to close the leaf contacts of the reed switch and the induction unit becomes operational.
Similarly, U.S. Pat. No. 3,993,885-Kominami et al includes a movable magnet, a fixed magnet and a reed switch situated between the two magnets. If a ferrous pan is placed upon the induction heating unit, the movable magnet is attracted towards the pan and the flux lines near the reed switch are changed so as to allow power to be supplied to the heating coil.
U.S. Pat. No. 4,013,859-Peters, Jr. utilizes a very low power oscillator coupled to a load sensing coil for indicating the presence of a pan above the work coil. Furthermore, U.S. Pat. Nos. 3,823,297-Cunningham; 4,016,392-Kobayashi et al; and 4,010,342-Austin include current or voltage detectors which also indicate the presence of a pan above the induction heating coil.
It has also been observed that the electromagnetic fields may be even further reduced by insuring that the ferromagnetic cooking utensil, in addition to being present above the work coil, is properly centered with respect to the induction coil. The strength of electromagnetic fields in the vicinity of the cooking surface, it has been observed, are dramatically increased merely by displacing the cooking utensil off-center with respect to the work coil.
However, while the above noted patents include detectors or sensors which would disable the inverter circuit of the induction work coil if no utensil was placed upon the cooking surfaces, none of these patents is directed to the problem of disabling the inverter circuit if a utensil is placed off-center upon the cooking surface with respect to the induction work coil.